(Not Applicable)
(Not Applicable)
The present invention pertains generally to steam desuperheaters and, more particularly, to a vortex generator of a steam desuperheater for reducing steam temperature by generating a closed vortex within a flow of superheated steam passing through a steam pipe and spraying the steam flow with cooling water.
Many industrial facilities operate with superheated steam that has a higher temperature than its saturation temperature at a given pressure. Because superheated steam can damage turbines or other downstream components, it is necessary to control the temperature of the steam. Desuperheating refers to the process of reducing the temperature of the superheated steam to a point near its saturation temperature, thereby increasing the system thermal efficiency, ensuring system protection, and correcting for unintentional amounts of superheat.
Conventional steam desuperheaters can lower the temperature of superheated steam by spraying cooling water into a steam pipe through a spray nozzle mounted on the wall of the steam pipe. The cooling water is sprayed into a flow of superheated steam that is passing through the steam pipe. Once the cooling water is sprayed into the flow of superheated steam, the cooling water mixes with the superheated steam and evaporates, drawing thermal energy from the steam and lowering its temperature. Ideally, the cooling water spray will enter the steam pipe as very fine water droplets in a spray pattern that will penetrate through the width of the steam pipe and evenly mix with the superheated steam flow. However, if the steam flow has a low velocity or if the cooling water spray is comprised of relatively large water droplets, then the cooling water spray may pass through the steam flow and impinge upon the opposite interior wall of the steam pipe. The resulting dispersion and mixing of the cooling water with the superheated steam flow is poor, resulting in a greatly diminished evaporation rate of the cooling water and an uneven and poorly controlled temperature reduction throughout the flow of the superheated steam. In addition, an impinging cooling water spray may result in water buildup on the interior wall of the steam pipe. This water buildup can cause erosion and thermal stresses in the steam pipe as the wall of the steam pipe can reach upwards of 1000xc2x0 F. Such thermal stresses may lead to structural failure of the steam pipe and other components. Furthermore, the accumulation of cooling water on the interior wall of the steam pipe will eventually evaporate in a non-uniform heat exchange between the water and the superheated steam, resulting in a poorly controlled temperature reduction. Finally, even if the cooling water spray does not impinge on the opposite wall of the steam pipe, the length of time for evaporation may be increased if the cooling water spray is comprised of large water droplets. This is because larger water droplets may have a longer evaporation time as compared to the evaporation time for smaller or finer water droplets. As a result of the increased evaporation time for the larger water droplets, the superheated steam must travel a longer distance in the steam pipe before achieving a uniform temperature reduction.
Various desuperheating devices have been developed to overcome these problems. One such prior art desuperheating device attempts to avoid these problems by spraying cooling water into the steam pipe at an angle to avoid impinging the walls of the steam pipe. However, the construction of this device is complex with many parts such that the device has a high construction cost. Another prior art desuperheating device utilizes a spray nozzle positioned in the center of the steam pipe with multiple nozzles and a moving plug or slide member uncovering an increasing number of nozzles. Each of the nozzles is in fluid communication with a cooling water source. Although this desuperheating device may eliminate the impingement of the cooling water spray on the steam pipe walls, such a device is necessarily complex, costly to manufacture and install and requires a high degree of maintenance after installation.
As can be seen, there exists a need in the art for a desuperheating device capable of increasing the velocity of the flow of superheated steam such that cooling water spray will not impinge on the walls of the steam pipe. Furthermore, there exists a need in the art for a desuperheating device capable of creating turbulent flow adjacent the cooling water spray nozzle to promote the uniform mixing of the cooling water with the superheated steam. Additionally, there exists a need in the art for a desuperheating device capable of increasing the velocity of the flow of superheated steam for more effective evaporation of cooling water sprayed into the steam pipe. Finally, there exists a need in the art for a desuperheating device for spraying cooling water into a flow of superheated steam that is of simple construction with relatively few components and requiring low maintenance.
The present invention specifically addresses and alleviates the above referenced deficiencies associated with steam desuperheaters. More particularly, the present invention is a vortex generator of a desuperheating device for generating a closed vortex within a flow of superheated steam passing through a steam pipe.
The vortex generator is configured to increase the velocity of the flow of superheated steam within a closed vortex and subsequently generates vortices and eddies in a recirculation zone. The vortices and eddies improve the mixing of the cooling water spray within the superheated steam. This feature is especially beneficial if the cooling water spray is comprised of relatively large water droplets because larger water droplets tend to penetrate deeper across the flow of superheated steam. However, because of the vortices and eddies within the closed vortex, the larger water droplets are captured and may then undergo evaporation due to the increased residence time of the water droplets within the closed vortex. The vortex generator is comprised of a diffuser, a vortex ring and a spray nozzle. The diffuser and the steam pipe together define an annular chamber within which is disposed the vortex ring. The diffuser increases the velocity of the superheated steam by forcing the flow of superheated steam through an array of orifices formed in a barrel section. An end plate seals the barrel section such that superheated steam must pass through the orifices. The end plate also creates an area of low pressure downstream of the diffuser which helps to create a swirling flow of superheated steam.
The vortex ring is disposed within the annular chamber at the downstream end of the barrel section and is configured to impart a spiraling motion to the flow of superheated steam that is exiting the annular chamber. The combination of the spiraling motion imparted to the superheated steam by the vortex ring, the increased velocity produced by the diffuser, and the low pressure area created by the end plate results in a spiraling, swirling flow of eddies and vortices in the low pressure area or recirculation zone. A spray nozzle mounted on the steam pipe sprays cooling water into the flow of superheated steam. The spray nozzle may be regulated by a control valve which may vary the rate of cooling water flowing out of the spray nozzle. Ideally, the spray nozzle is positioned such that the cooling water is sprayed directly into the low pressure area where the superheated steam is in a spiraling, swirling flow of eddies and vortices. The spray nozzle causes the cooling water to enter the steam pipe in a pattern of spray consisting of very small water droplets. The spray pattern maximizes the surface area of the cooling water spray, permitting more effective evaporation of the cooling water. This spray pattern promotes the uniform mixing of the cooling water with the steam flow and thus optimizes the desuperheating effect per unit mass of cooling water.